Check off each step as you cook.

1. 01Mix and raise the dough.Mix flour, yeast, dough sugar, and salt. Add lukewarm milk, melted dough butter, the whole egg, and the separated yolk; reserve the white in the refrigerator. Knead for 8–10 minutes until supple, using a little extra flour only if very sticky. Cover and leave in a warm place for about 75 minutes until doubled.
2. 02Cook and grind the seeds.While the dough rises, put poppy seeds and measured water in a saucepan. Bring to a boil, turn off the heat, and soak for 20 minutes. Return to a gentle simmer for 20–25 minutes, adding water if needed to keep the seeds covered. Drain in a fine cloth-lined sieve and press out excess liquid. Let cool for about 15 minutes, then grind twice through a fine meat-grinder plate or use a poppy-seed mill according to its instructions.
3. 03Finish the filling.Warm filling butter in a pan and stir in ground poppy seeds, filling sugar, honey, raisins, and walnuts. Cook over low heat for 3–4 minutes until combined and no loose liquid remains. Spread in a shallow bowl and allow about 20 minutes to cool fully before stirring in the reserved egg white. Never put hot filling onto the yeast dough.
4. 04Shape the spiral.Roll the dough on a lightly floured surface to a rectangle roughly 12 by 14 inches / 30 by 35 cm for each base-size roll. Spread filling evenly, leaving a ¾-inch / 2 cm border. Roll from a short edge to make a log about 12 inches / 30 cm long. Pinch the seam and tuck the ends underneath.
5. 05Give it a final rise.Place seam-side down on parchment. Loosely wrap the parchment around the roll, leaving about ¾ inch / 2 cm of room for expansion and keeping the paper seam underneath. Place on a baking tray and let rise for about 40 minutes. Heat the oven to 350°F / 180°C during this rise.
6. 06Bake and cool.Bake for 40–45 minutes until the dough is deeply golden and cooked through; the center of the filling should reach at least 160°F / 71°C. Unwrap carefully and cool on a rack for at least 1 hour before glazing. If the filling needs longer to cool during preparation, allow that extra time too.
7. 07Glaze lightly.Mix powdered sugar with lemon juice, adding water a few drops at a time to make a thick, slowly flowing glaze. Drizzle over the cooled roll, let it settle, then cut with a serrated knife.

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